Abstract: Modified polyester fiber reinforced concrete with different additions was prepared. The dispersivity of modified polyester fibers in concrete by five different mixing methods was studied by an image processing method. With a series of durability tests, the carbonation resistance, chloride penetration resistance and frost resistance of the fiber reinforced concrete were also investigated. The results indicate that the image processing method can evaluate the dispersivity of the fiber reinforced concrete well. The mixing method of "aggregate and binding materials for 60 s + water for 60 s + fiber for 60 s" makes the best dispersivity of modified polyester fibers. It is in accord with direct observations by naked eyes. The compressive strength is increased by the addition of modified polyester fibers. After adding 1.1 kg·m^-3 modified polyester fibers, the compressive strength of concrete increases by 14%; but with more modified polyester fibers, the compressive strength no longer increases. The existence of modified polyester fibers in concrete can slow down the diffusion of CO₂, the carbonation rate of concrete decreases by 12.6% to 18.9%, and with more modified polyester fibers, the carbonation resistance became better. After the addition of modified polyester fibers, the chloride diffusion coefficient of concrete also decreases. The modified polyester fibers can reduce the surface spalling of concrete during freeze-thaw cycles, which improves the frost resistance of concrete significantly.